Communication system

ABSTRACT

A communication system is disclosed, in which a mobile telephone has a control-plane connection to a first base station and communicates user data using at least one communication bearer provided via a second base station. The base stations are configured to exchange information relating to the data rate required for the mobile telephone via the second base station. The first base station derives, based on the exchanged information, an aggregated maximum bit rate (AMBR) parameter specific to the second base station and provides the derived AMBR parameter to the second base station for use in data rate enforcement for the mobile telephone&#39;s communications via the second base station.

The present application is a continuation application of U.S. patentapplication Ser. No. 15/500,218 filed on Jan. 30, 2017, which is aNational Stage Entry of international application PCT/JP2015/003641,filed Jul. 21, 2015, which claims the benefit of priority from UnitedKingdom Patent Application 1414139.4 filed on Aug. 8, 2014, thedisclosures of all of which are incorporated in their entirety byreference herein.

TECHNICAL FIELD

The present invention relates to a communication system and tocomponents thereof for providing communication services to mobile orfixed communication devices. The invention has particular, but notexclusive, relevance to connectivity via multiple base stations in LongTerm Evolution (LTE) Advanced systems as currently defined in associated3^(rd) Generation Partnership Project (3GPP) standards documentation.

BACKGROUND ART

In a cellular communications network, user equipment (UE) (such asmobile telephones, mobile devices, mobile terminals, etc.) cancommunicate with other user equipment and/or remote servers via basestations. LTE systems include an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN) and an Evolved Packet Core (EPC) network (orsimply ‘core network’). The E-UTRAN includes a number of base stations(‘eNBs’) for providing both user-plane (e.g. Packet Data ConvergenceProtocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC)and PHYsical (PHY) layers) and control-plane (e.g. Radio ResourceControl (RRC)) protocol terminations towards the UE.

Recent developments in communication networks have seen increaseddeployment of so called ‘small’ cells operated by Low Power Nodes(LPNs), such as pico eNBs, femto eNBs, home eNBs (HeNBs) or the like,which cells have a smaller coverage area than existing macro cellsoperated by a higher power (regular) macro base station. Networkscomprising a number of different cell types, for example a networkcomprising a macro cell and a femto cell, are referred to asHeterogeneous Networks, or HetNets. In the following description theterm base station is used to refer to any such macro base station orLPN.

Conventionally, a mobile telephone is configured to communicate via onebase station (using an associated radio link). However, in a study onsmall cell enhancements for E-UTRA and E-UTRAN (3GPP technical report(TR) no. 36.842, the contents of which are incorporated herein byreference), a so-called ‘dual connectivity’ functionality was introducedto improve, for example, the coverage of high data rates for userequipment, temporary network deployment, cell edge throughput and/or toincrease system throughput. The dual connectivity feature establishedtechniques for compatible mobile telephones (and other user equipment)to communicate with multiple network points, substantiallysimultaneously. Specifically, this ‘dual connectivity’ functionalityrefers to an operation mode where a given mobile telephone (operating inRRC_CONNECTED mode) consumes radio resources provided by at least twodifferent network points (e.g. two or more base stations). Typically,one of the network points involved in the dual connectivityfunctionality is a macro base station and the other network point (or aplurality of network points) comprises a low power node (or plurality oflow power nodes).

Each network point (also referred to as ‘access point’) involved in theprovision of dual connectivity for a mobile telephone may assume adifferent role. One of the network points may be referred to as a masterbase station (MeNB) and each one of the other network points may bereferred to as a secondary base station (SeNB). Typically, the varioussecondary base stations involved in the provision of dual connectivityare coupled (to the MeNB and hence the core network) via a so-callednon-ideal backhaul. Further, in a dual connectivity scenario, one of thebase stations (the MeNB) routes control plane signaling to the corenetwork via an associated interface (e.g. the S1 interface), regardlessof whether or not the other base station is also connected to the corenetwork for user plane communication (e.g. to a serving gateway).

The MeNB/SeNB roles do not necessarily depend on each base station'scapabilities/type (e.g. power class) and may be different for differentmobile telephones (even when using the same base stations).

In accordance with the dual connectivity functionality, a mappingbetween the mobile telephone's radio (communication) bearer(s) and thebase stations may be realised as follows:

-   -   a so-called Master Cell Group (MCG) bearer in which a radio        bearer is served by the MeNB only (or ‘MeNB-specific bearer’);    -   a so-called Secondary Cell Group (SCG) bearer in which a radio        bearer is served by the SeNB only (or ‘SeNB-specific bearer’);        and    -   a split bearer in which a radio bearer is served by the MeNB and        the SeNB.

In order to ensure that an appropriate level of service (e.g. a desireddata rate) can be provided for each user in the communication network,the network operator assigns various parameters that determine anaggregate maximum bit rate (AMBR) that can be provided to the users(subscribers) in the network per subscriber and per access point.Specifically, for each subscriber, the Home Subscriber Server (HSS)holds an associated ‘HSS_APN-AMBR’ parameter (per APN) and an‘HSS_UE-AMBR’ parameter, forming part of the user's subscription data.

The HSS_APN-AMBR (APN Aggregate Maximum Bit Rate) parameter for aparticular (subscriber's) user communication device limits thenon-guaranteed aggregate bit rate across all PDN connections by thatuser communication device via a particular APN. The actual ‘APN-AMBR’parameter to be used (enforced) by the given access point (e.g. P-GW) isprovided by the MME based on subscription data obtained from the HSS.

The HSS_UE-AMBR (UE Aggregate Maximum Bit Rate) parameter for aparticular (subscriber's) user communication device limits the totaltraffic of that user communication device on uplink and downlink (viathe serving base station). The actual ‘UE-AMBR’ parameter to be used(enforced) by the serving base station is provided by the MME based onsubscription data obtained from the HSS. Specifically, the MME computesthe UE-AMBR parameter such that it equals the smaller of the sum of allHSS_APN-AMBR parameters of active APNs and the HSS-UE-AMBR parameter.This is further illustrated in the 3GPP TS 23.401 standard, the contentsof which are incorporated herein by reference. The MME transmits thecalculated UE-AMBR parameter to the serving base station, which basestation is thus able to allow/discard data traffic for the usercommunication device in accordance with the UE-AMBR parameter. This isfurther illustrated in the 3GPP TS 36.413 and TS 36.300 standards, thecontents of which are incorporated herein by reference.

Thus traffic sent/received by a particular user communication device inexcess of the bit rate indicated by the UE-AMBR parameter may getdiscarded by a rate shaping function of the base station serving thatuser communication device, and traffic exceeding the bit rate indicatedby the applicable APN-AMBR parameter may get discarded by a rate shapingfunction of the corresponding APN. The UE-AMBR parameter and theAPN-AMBR parameter are applicable across all non-Guaranteed Bit Rate(non-GBR) bearers of a particular subscriber (i.e. a user communicationdevice associated with that subscriber).

Each base station guarantees a downlink guaranteed bit rate associatedwith a so-called guaranteed bit rate (GBR) bearer, enforces a downlinkmaximum bit rate (MBR) associated with a particular GBR bearer andenforces a downlink Aggregate Maximum Bit Rate (AMBR) associated with agroup of non-GBR bearers. Further, in the uplink, by limiting the totalgrant of communication resources to an item of user equipment, the basestation can ensure that a UE-AMBR for a respective group of non-GBRbearers associated with each item of user equipment, plus the sum ofMBRs is not exceeded.

There is a general consensus that, during dual connectivity, the MeNBshould manage the UE-AMBR and provide, to the SeNB, information whichassists the SeNB to provide both downlink and uplink AMBR enforcementwhen the SCG bearer option is applied.

The overall UE-AMBR enforced for a particular dual connectivity UE maybe split between an MeNB-specific UE-AMBR (M_(UE-AMBR)) for that UE andan SeNB-specific UE-AMBR (S_(UE-AMBR)) for that UE. The S_(UE-AMBR) issent to the SeNB by the MeNB managing the overall UE-AMBR, and the SeNBenforces the S_(UE-AMBR) accordingly.

However, the inventors have realised that, as a result of non-GBRbearers of a UE potentially being distributed between the MeNB and SeNBduring dual connectivity, and contrary to the current consensus, thegenerally accepted route forward can result in a sub-optimal solution inwhich, for example, the UE-AMBR is not always split between the masterand secondary base stations in the most efficient manner.

For example, when there is a lot of data in SeNB's buffer which is notsent due to enforcement of the S_(UE-AMBR), and the data rate of dataarriving in MeNB is significantly lower than M_(UE-AMBR), then theactual data rate available to the UE may be significantly lower than theoverall UE-AMBR that the UE is entitled to by contract. Similarly, whenthere is a lot of data in MeNB's buffer which is not sent due toenforcement of the M_(UE-AMBR), and the data rate of data arriving inSeNB is significantly lower than S_(UE-AMBR), then the actual data rateavailable to the UE may be significantly lower than the overall UE-AMBRthat the UE is entitled to by contract. Thus, the UE may suffer dataloss due to UE-AMBR enforcement unnecessarily.

To help illustrate this issue, a number of examples of unnecessary dataloss are summarises below:

Downlink—Unnecessary Packet Dropping in SeNB:

For a particular UE, the value of UE-AMBR may be e.g. 10 Mbps fordistribution between the two radio bearers used by the UE (e.g. E-RAB#1provided via the MeNB and E-RAB#2 provided via the SeNB). In this case,for example, the following parameters may be configured (for the UE'snon-GBR bearers):

M_(UE-AMBR)=5 Mbps (for communication bearers over E-RAB#1 via the MeNB)

S_(UE-AMBR)=5 Mbps (for communication bearers over E-RAB#2 via the SeNB)

However, when E-RAB#1 has almost no activity but the communicationbearers over E-RAB#2 carry a large amount of data, it is possible thatthe aggregated data rate for E-RAB#2 may exceed the allowed 5 Mbps. Inthis case, therefore, the SeNB enforces the S_(UE-AMBR) by dropping datapackets for the UE that are determined to be above the user's allowance(S_(UE-AMBR)). This may result, from a user point of view, in the UEonly receiving an effective 5 Mbps (assuming that E-RAB#1 has noactivity and S_(UE-AMBR) for E-RAB#2 is set to 5 Mbps) while thecontracted UE-AMBR is 10 Mbps.

Downlink—Unnecessary Packet Dropping in MeNB:

Similarly, using the parameters of the previous example (M_(UE-AMBR)=5Mbps and S_(UE-AMBR)=5 Mbps), there may be scenarios in which the MeNBmay drop data packets for a particular UE unnecessarily.

For example, when E-RAB#2 via the SeNB has almost no activity but thecommunication bearers provided over E-RAB#1 carry a large amount ofdata, it is possible that the aggregated data rate for E-RAB#1 mayexceed the allowed 5 Mbps via that base station (MeNB). The MeNB maythus start dropping data packets resulting, from a user point of view,in the UE only receiving an effective 5 Mbps while its contractedUE-AMBR is 10 Mbps.

It will be appreciated that similar scenarios are also possible for theenforcement of uplink UE-AMBRs.

In summary, when the communication bearers for a particular UE in dualconnectivity exhibit an imbalance (at least temporarily) between thebase stations serving the UE, it may be difficult or impossible toensure that the aggregated data rate for a particular UE meets the datarate (UE-AMBR) associated with the user's subscription.

SUMMARY OF INVENTION

Accordingly, preferred embodiments of the present invention aim toprovide methods and apparatus which overcome or at least partiallyalleviate at least one of the above issues.

In one aspect, the invention provides a base station configured tooperate as part of a dual connectivity configuration in which acontrol-plane connection for a user communication device is provided viathe base station and at least one communication bearer between a corenetwork and the user communication device is provided via at least afurther base station, said base station comprising: means for obtainingan aggregate maximum bit rate specific to said user communication deviceand for obtaining information relating to a data rate required for saiduser communication device via said further base station; means forgenerating information identifying a bit rate specific to said furtherbase station, for use in enforcement of an aggregate maximum datathroughput for said user communication device via said further basestation, wherein said bit rate specific to said further base station isgenerated based on: i) said aggregate maximum bit rate specific to saiduser communication device; and ii) said obtained information relating toa data rate required for said user communication device via said furtherbase station; and means for providing, to said further base station,said information identifying said bit rate specific to said further basestation.

In one aspect, the invention provides a secondary base stationconfigured to operate as part of a dual connectivity configuration inwhich a control-plane connection for a user communication device isprovided via a master base station, different to said secondary basestation, and at least one communication bearer between a core networkand the user communication device is provided via said secondary basestation, said secondary base station comprising: means for determining adata rate required for said user communication device via said secondarybase station; means for providing, to said master base station,information relating to said determined data rate required for said usercommunication device via said secondary base station; and means forreceiving, from said master base station, information identifying a bitrate specific to said secondary base station, wherein said bit ratespecific to said secondary base station is based on: i) an aggregatemaximum bit rate specific to said user communication device; and ii)said data rate required for said user communication device via saidsecondary base station.

In one aspect, the invention provides a system comprising the abovedescribed base station, the above described secondary base station, anda user communication device.

In one aspect, the invention provides a method performed by a basestation configured to operate as part of a dual connectivityconfiguration in which a control-plane connection for a usercommunication device is provided via the base station and at least onecommunication bearer between a core network and the user communicationdevice is provided via at least a further base station, the methodcomprising: obtaining an aggregate maximum bit rate specific to saiduser communication device, and information relating to a data raterequired for said user communication device via said further basestation; generating information identifying a bit rate specific to saidfurther base station, for use in enforcement of a maximum datathroughput for said user communication device via said further basestation, wherein said bit rate specific to said further base station isgenerated based on: i) said aggregate maximum bit rate specific to saiduser communication device; and ii) said obtained information relating toa data rate required for said user communication device via said furtherbase station; and providing, to said further base station, saidinformation identifying said bit rate specific to said further basestation.

In one aspect, the invention provides a method performed by a secondarybase station configured to operate as part of a dual connectivityconfiguration in which a control-plane connection for a usercommunication device is provided via a master base station, different tosaid secondary base station, and at least one communication bearerbetween a core network and the user communication device is provided viasaid secondary base station, the method comprising: determining a datarate required for said user communication device via said secondary basestation; providing, to said master base station, information relating tosaid determined data rate required for said user communication devicevia said secondary base station; and receiving, from said master basestation, information identifying a bit rate specific to said secondarybase station, wherein said bit rate specific to said secondary basestation is based on: i) an aggregate maximum bit rate specific to saiduser communication device; and ii) said data rate required for said usercommunication device via said secondary base station.

The invention provides, for all methods disclosed, correspondingcomputer programs or computer program products for execution oncorresponding equipment, the equipment itself (user equipment, nodes orcomponents thereof) and methods of updating the equipment.

Each feature disclosed in this specification (which term includes theclaims) and/or shown in the drawings may be incorporated in theinvention independently (or in combination with) any other disclosedand/or illustrated features. In particular but without limitation thefeatures of any of the claims dependent from a particular independentclaim may be introduced into that independent claim in any combinationor individually.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the attached figures in which:

FIG. 1 schematically illustrates a mobile telecommunication system of atype to which the invention is applicable;

FIG. 2 is a block diagram illustrating the main components of the mobiletelephone forming part of the system shown in FIG. 1;

FIG. 3 is a block diagram illustrating the main components of the masterbase station forming part of the system shown in FIG. 1;

FIG. 4 is a block diagram illustrating the main components of thesecondary base station forming part of the system shown in FIG. 1;

FIG. 5 illustrates an exemplary way in which dual connectivity can beprovided in the system shown in FIG. 1 using an SeNB-specific bearer;

FIG. 6 is an exemplary timing diagram illustrating a procedure performedby elements of the mobile telecommunication system; and

FIG. 7 illustrates a modification of the procedure shown in FIG. 6.

FIG. 8 illustrates another modification of the procedure shown in FIG.6.

DESCRIPTION OF EMBODIMENTS

<Overview>

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 including a mobile telephone 3 (or other compatiblecommunication device/user equipment) served via the base stations 5-1and 5-2. As those skilled in the art will appreciate, whilst one mobiletelephone 3 and two base stations 5 are shown in FIG. 1 for illustrationpurposes, the system, when implemented, will typically include otherbase stations and mobile telephones.

A user of the mobile telephone 3 can communicate with other users and/orremote servers via the base stations 5 and the core network 7. The corenetwork 7 comprises, amongst other things, a mobility management entity(MME) 11, a serving gateway (S-GW) 13, and a Packet Data Network (PDN)Gateway (P-GW) 15.

The MME 11 manages general mobility aspects of the mobile telephone 3and ensures that connectivity is maintained with the mobile telephone 3as it is moving within the geographical area covered by thecommunication system (and/or as the mobile telephone 3 is handed overbetween base stations of the communication system). The MME 11 alsohandles control-plane signaling for the mobile telephone 3 and managesthe various bearers associated with the mobile telephone 3 (e.g. such asan Evolved Packet System (EPS) bearer and/or a radio bearer) e.g. bycontrolling the S-GW 13 and the P-GW 15 (and/or possibly other networknodes) via which such bearers are provided.

The S-GW 13 provides a connection between the mobile telephone 3 and thecore network 7 (via the base station 5-1) for sending and receiving userplane data over an associated communication bearer (e.g. an EPS bearer).The communication bearer normally terminates at the P-GW 15, although itis often complemented by an external bearer as well (for example,another EPS bearer and/or the like) between the P-GW 15 and acommunication end-point outside the core network 7 (e.g. in an externalnetwork 20). It will be appreciated that, whilst shown as separateentities, the functionalities of the S-GW 13 and the P-GW 15 could beimplemented in a single gateway element.

As will be understood by those skilled in the art, each base station 5operates one or more base station cells (not shown) in whichcommunications can be made between the base station 5 and the mobiletelephone 3 using one or more suitable communication links (e.g. radiolinks) provided between the mobile telephone 3 and the respectiveserving base station 5. Each of the communication links may be carriedover one or more associated component carriers (F1, F2).

In this system, a dual connectivity service can be provided tocompatible user equipment (such as the mobile telephone 3) using anappropriately configured communication bearer or bearers (e.g. asspecified in 3GPP TR 36.842). In the case of dual connectivity, one ofthe base stations is configured as a master base station (MeNB) 5-1 andthe other base station is configured as a secondary base station (SeNB)5-2. The base stations 5 are connected to each other via an appropriatebase station to base station communication interface (e.g. an ‘X2’interface). In this example, the base stations 5 are connected to eachother using a non-ideal backhaul.

The MeNB 5-1 is connected to the core network 7 via an S1 interface inorder to provide both user-plane (‘S1-U’) communication via the S-GW 13(for MeNB-specific bearers and any split bearers) and control-plane(‘S1-MME’) communication with the MME 11 (for all bearers). The SeNB 5-2is also connected to the core network 7 via an appropriate S1 interfacein order to provide user-plane (‘S1-U’) communication over at least someof its communication bearers (e.g. SeNB-specific bearers). Although inFIG. 1 the SeNB 5-2 is shown to be connected to the core network 7directly, it may also be connected indirectly, e.g. via the externalnetwork 20. Although not shown in FIG. 1, the SeNB 5-2 may also haveuser-plane (‘S1-U’) connectivity via the MeNB 5-1 over the non-idealbackhaul (e.g. when using a split bearer configuration).

The mobile telephone 3 may be configured with multiple communicationbearers (for example, a first communication bearer for voice, a secondcommunication bearer for video, a third communication bearer forinternet data, etc.), e.g. in order to provide different transmissionpriorities for different services. Each communication bearer (and eachdata packet sent over the communication bearers) is associated with anappropriate quality of service (QoS) identifier, such as a QoS classindicator (QCI) value, in order ensure that the appropriate transmissionpriorities can be met regardless whether such communication bearers areprovided via the MeNB 5-1, the SeNB 5-2, or both. Data associated withone of the mobile telephone's 3 communication bearers may be transmittedon the same radio link/carrier (although data for different bearers maybe transmitted over different radio links/carriers).

In this system, the base stations 5-1, 5-2 (and the mobile telephone 3)are configured to provide dual connectivity using at least anSeNB-specific bearer, i.e. a communication bearer served via the SeNB5-2 for communicating user-plane data for the mobile telephone 3. Thesetting up of such a bearer may be initiated by the MeNB 5-1, whenappropriate. As part of this dual connectivity service, in this example,PDCP, RLC, MAC, and PHY functionalities for the communication bearer areprovided by the SeNB 5-2. Thus, when a downlink data packet is receivedby the SeNB 5-1 (from the core network 7 over the S1 interface), theSeNB 5-1 performs appropriate processing of the data packet (and passesthe data packet from the PDCP layer to the lower layers) fortransmission towards the mobile telephone 3.

Advantageously, the base stations 5-1, 5-2 are also configured toenforce an associated aggregate maximum bit rate (i.e. UE-AMBR)parameter for the non-GBR communications of the mobile telephone 3.Specifically, the MeNB 5-1 obtains the value of the UE-AMBR from the MME11 when it is setting up an initial context for the mobile telephone 3,e.g. as part of a connection establishment procedure between the mobiletelephone 3 and the base station 5-1. The MeNB 5-1 is also configured toderive, from the obtained UE-AMBR, the applicable aggregate maximum bitrates M_(UE-AMBR) and S_(UE-AMBR) for the MeNB 5-1 and the SeNB 5-2,respectively. In this case, the M_(UE-AMBR) and the S_(UE-AMBR) may bechosen such that their sum is equal to the UE-AMBR, which ensures thatthe mobile telephone 3 does not exceed its associated aggregate maximumbit rate even when it is using a dual connectivity service.

For example, the MeNB 5-1 may be configured to derive, from the overallUE-AMBR to be enforced for a particular dual connectivity UE, anMeNB-specific UE-AMBR (M_(UE-AMBR)) for that UE and an SeNB-specificUE-AMBR (S_(UE-AMBR)) for that UE based on the following equation:

UE-AMBR=M _(UE-AMBR) +S _(UE-AMBR)

Each base station 5-1 and 5-2 is responsible for ensuring that anappropriate (base station specific) aggregate maximum bit rate isenforced for the mobile telephone 3 connected to that base station.Thus, the MeNB 5-1 enforces the M_(UE-AMBR) for the mobile telephone's 3communications via the MeNB's 5-1, and the SeNB 5-2 enforces theS_(UE-AMBR) for the mobile telephone's 3 communications via the SeNB's5-2.

Advantageously, in this example, the MeNB 5-1 is operable to obtain,from the SeNB 5-2, information relating to a current data rate for themobile telephone 3 via the SeNB 5-2. The obtained information maycomprise, for example, a data rate value measured at the SeNB 5-2, anindication that the data rate (via the SeNB 5-2) is above apredetermined threshold, an indication that a transmission buffer at theSeNB 5-2 is above a predetermined threshold, an indication that apredetermined number of data packets (e.g. at least one data packet) hasbeen dropped at the SeNB 5-2, and/or the like. The information (datarate/indication) provided by the SeNB 5-2 may relate to the non-GBRbearers associated with the mobile telephone 3 at the SeNB 5-2, althoughit may relate to other bearers as well.

When appropriate, the MeNB 5-1 is beneficially able to update theapplicable M_(UE-AMBR) and/or S_(UE-AMBR) based on the informationobtained from the SeNB 5-2 and provide an updated S_(UE-AMBR) to theSeNB 5-2.

For example, when the obtained information indicates that the mobiletelephone's 3 data rate via the SeNB 5-2 is likely to exceed (or hasexceeded) the associated data rate allowance (S_(UE-AMBR)), and the MeNB5-1 determines that its own data rate is (at least momentarily) belowthe associated data rate allowance (M_(UE-AMBR)), the MeNB 5-1 is ableto update the applicable M_(UE-AMBR) and/or S_(UE-AMBR) parameters toalleviate the risk of a potential drop of data packets at the SeNB 5-2.For example, the MeNB 5-1 may decrease the value of the M_(UE-AMBR)parameter and increase the value of the S_(UE-AMBR) parameter (butensuring that UE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)). Once an updatedS_(UE-AMBR) parameter is derived by the MeNB 5-1, it is forwarded to theSeNB 5-2 (over the X2 interface) so that the SeNB 5-2 can apply theupdated S_(UE-AMBR) parameter to the mobile telephone's 3 subsequentcommunications via the SeNB 5-2.

Similarly, when the obtained information indicates that the mobiletelephone's 3 data rate via the SeNB 5-2 is below the associated datarate allowance (S_(UE-AMBR)), and the MeNB 5-1 determines that its owndata rate is (at least momentarily) is about to exceed the associateddata rate allowance (M_(UE-AMBR)), the MeNB 5-1 is able to update theapplicable M_(UE-AMBR) and/or S_(UE-AMBR) parameters to alleviate therisk of a potential drop of data packets at the MeNB 5-1. For example,the MeNB 5-1 may increase the value of the M_(UE-AMBR) parameter anddecrease the value of the S_(UE-AMBR) parameter (but ensuring thatUE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)). Once an updated S_(UE-AMBR) parameteris derived by the MeNB 5-1, it is forwarded to the SeNB 5-2 (over the X2interface) so that the SeNB 5-2 can apply the updated S_(UE-AMBR)parameter to the mobile telephone's 3 subsequent communications via theSeNB 5-2.

In summary, when the communication bearers for a particular UE in dualconnectivity exhibit an imbalance (at least temporarily) between thebase stations serving the UE, it is possible to ensure, based on theinformation exchanged between the base stations 5-1 and 5-2, that theaggregated data rate for a particular UE (via all base stations involvedin the dual connectivity service) meets the data rate (UE-AMBR)associated with the user's subscription.

<Mobile Telephone>

FIG. 2 is a block diagram illustrating the main components of the mobiletelephone 3 shown in FIG. 1. As shown, the mobile telephone 3 has atransceiver circuit 31 that is operable to transmit signals to and toreceive signals from a base station 5 via one or more antenna 33. Themobile telephone 3 has a controller 37 to control the operation of themobile telephone 3. The controller 37 is associated with a memory 39 andis coupled to the transceiver circuit 31. Although not necessarily shownin FIG. 2, the mobile telephone 3 may of course have all the usualfunctionality of a conventional mobile telephone 3 (such as a userinterface 35) and this may be provided by any one or any combination ofhardware, software and firmware, as appropriate. Software may bepre-installed in the memory 39 and/or may be downloaded via thetelecommunications network or from a removable data storage device(RMD), for example.

The controller 37 is configured to control overall operation of themobile telephone 3 by, in this example, program instructions or softwareinstructions stored within memory 39. As shown, these softwareinstructions include, among other things, an operating system 41, acommunications control module 43, and a dual connectivity module 45.

The communications control module 43 controls communications between themobile telephone 3 and the base station(s) 5. The communications controlmodule 43 also controls the separate flows of uplink data and downlinkdata and control data to be transmitted to the base station 5 (and othernodes, e.g. the MME 11, via the base station 5).

The dual connectivity module 45 coordinates (with assistance by thecommunications control module 43) communications over the respectivecommunication bearer(s) forming part of a dual connectivity service. Thedual connectivity module 45 also controls communications with the MeNB5-1 over the associated carrier F1 and communications with the SeNB 5-2over the associated carrier F2.

<Master Base Station>

FIG. 3 is a block diagram illustrating the main components of the masterbase station 5-1 shown in FIG. 1. The master base station 5-1 is acommunications node providing services to user equipment 3 within itscoverage area. In the embodiments according to the invention,communications between the various base stations 5 and the mobiletelephone 3 are coordinated. As shown, the master base station 5-1includes a transceiver circuit 51 which transmits signals to, andreceives signals from, the mobile telephone 3 via at least one antenna53. The master base station 5-1 also transmits signals to and receivessignals from the core network 7 and other neighbouring base stations(e.g. the SeNB 5-2) via a network interface 55 (X2/non-ideal backhaulinterface for communicating with neighbouring base stations and S1interface for communicating with the core network 7). The operation ofthe transceiver circuit 51 is controlled by a controller 57 inaccordance with software stored in memory 59. The software includes,among other things, an operating system 61, a communications controlmodule 63, a dual connectivity module 65, an S1 module 67, an X2 module68, and an AMBR module 69.

The communications control module 63 controls communications between themaster base station 5-1 and the SeNB 5-2, the mobile telephone 3, andthe core network devices.

The dual connectivity module 65 coordinates communications over thecommunication bearer (or bearers) forming part of a dual connectivityservice for the mobile telephone 3 served by this base station.

The dual connectivity module 65 includes the PDCP, RLC, MAC, and PHYentities (layers) responsible for communicating data packets (thatbelong to MeNB-specific bearers) via the base station 5-1 when it isconfigured as an MeNB.

The S1 module 67 handles S1 signaling (e.g. generates, sends, andreceives messages/PDUs formatted in accordance with the S1 protocol)between the base station 5 and the core network 7 entities (such as theMME 11 and the S-GW 13). For example, the S1 module 67 is responsiblefor receiving downlink data packets from the core network 7 and passingthe received data packets to the dual connectivity module 65 (via thePDCP entity), when the base station 5-1 is configured to operate as anMeNB.

The X2 module 68 handles X2 signaling (e.g. generates, sends, andreceives messages/PDUs formatted in accordance with the X2 applicationprotocol) between the master base station 5 and other base stations,such as the secondary base station 5-2. For example, the X2 module 68 isresponsible for exchanging, with the corresponding X2 module of thesecondary base station 5-2, signaling (e.g. control signaling and/ordata packets) relating to the SeNB-specific bearer.

The AMBR module 69 is responsible for ensuring that an appropriateaggregate maximum bit rate is enforced for the data packets transmittedfor each items of user equipment (such as the mobile telephone 3) servedby this base station (either directly, or indirectly, via another basestation as part of a dual connectivity service). In order to do so, theAMBR module 69 obtains, from the MME 11 and for each mobile telephone 3served by this base station 5-1, information identifying the aggregatemaximum bit rate allowed (e.g. subscribed) for the user associated withthat mobile telephone 3. When dual connectivity is configured for aparticular mobile telephone 3, the AMBR module 69 determines theapplicable aggregate maximum bit rates M_(UE-AMBR) and S_(UE-AMBR) foruse in enforcement of a maximum throughput for the mobile telephone's 3non-GBR communication bearers at the MeNB 5-1 and the SeNB 5-2,respectively. The AMBR module 69 enforces the M_(UE-AMBR) for the MeNB's5-1 communications with the mobile telephone 3 (e.g. for MeNB-specificbearers), and provides (via the X2 module 68) the applicable S_(UE-AMBR)to the SeNB 5-2 (for SeNB-specific bearers, and optionally splitbearers).

In some embodiments, the AMBR module 69 is configured to obtain (e.g.via the X2 module 68) information relating to a current data rate forthe mobile telephone 3 via the SeNB 5-2. The obtained information maycomprise, for example, a data rate value measured at the SeNB 5-2, anindication that the data rate (via the SeNB 5-2) is above apredetermined threshold, an indication that a transmission buffer at theSeNB 5-2 is above a predetermined threshold, an indication that apredetermined number of data packets (e.g. at least one data packet) hasbeen dropped at the SeNB 5-2, and/or the like. When appropriate, theAMBR module 69 updates the applicable M_(UE-AMBR) and/or S_(UE-AMBR)based on the information obtained from the SeNB 5-2 and provides theupdated S_(UE-AMBR) to the SeNB 5-2.

<Secondary Base Station>

FIG. 4 is a block diagram illustrating the main components of thesecondary base station 5-2 shown in FIG. 1. The secondary base station5-2 is a communications node providing services to user equipment 3within its coverage area. As shown, the secondary base station 5-2includes a transceiver circuit 51 which transmits signals to, andreceives signals from, the mobile telephone 3 via at least one antenna53. The secondary base station 5-2 also transmits signals to andreceives signals from the core network 7 and other neighbouring basestations (e.g. the MeNB 5-1) via a network interface 55 (X2/non-idealbackhaul interface for communicating with neighbouring base stations andan optional S1 interface for communicating with the core network 7). Theoperation of the transceiver circuit 51 is controlled by a controller 57in accordance with software stored in memory 59. The software includes,among other things, an operating system 61, a communications controlmodule 63, a dual connectivity module 65, an S1 module 67, an X2 module68, and an AMBR module 69.

The communications control module 63 controls communications between thesecondary base station 5-2 and the MeNB 5-1, the mobile telephone 3, andthe core network devices.

The dual connectivity module 65 coordinates communications over thecommunication bearer (or bearers) forming part of a dual connectivityservice for the mobile telephone 3 served by this base station.

The dual connectivity module 65 includes the PDCP, RLC, MAC, and PHYentities (layers) responsible for communicating data packets via thebase station 5-2 when it is configured as an SeNB.

The S1 module 67 handles S1 signaling (e.g. generates, sends, andreceives messages/PDUs formatted in accordance with the S1 protocol)between the base station 5 and the core network 7 entities (such as theMME 11 and the S-GW 13).

The X2 module 68 handles X2 signaling (e.g. generates, sends, andreceives messages/PDUs formatted in accordance with the X2 applicationprotocol) between the secondary base station 5-2 and other basestations, such as the master base station 5-1. For example, the X2module 68 is responsible for exchanging, with the corresponding X2module of the master base station 5-1, signaling (e.g. controlsignaling) relating to the SeNB-specific bearer.

The AMBR module 69 is responsible for ensuring that an appropriateaggregate maximum bit rate is enforced for the data packets transmittedfor each items of user equipment (such as the mobile telephone 3)connected to this base station 5-2 whilst configured as an SeNB. Inorder to do so, the AMBR module 69 obtains, from the MeNB 5-1 and foreach mobile telephone 3 served by this base station 5-2, informationidentifying the aggregate maximum bit rate allowed (S_(UE-AMBR)) forthat mobile telephone 3 via the base station 5-2 (for the mobiletelephone's 3 SeNB-specific bearers). The AMBR module 69 enforces theS_(UE-AMBR) for the SeNB's 5-2 communications with the mobile telephone3.

In some embodiments, the AMBR module 69 is configured to obtain (e.g.from the dual connectivity module 65) information relating to a currentdata rate for the mobile telephone 3 via the SeNB 5-2. The obtainedinformation may comprise, for example, a data rate value measured at theSeNB 5-2, an indication that the data rate (via the SeNB 5-2) is above apredetermined threshold, an indication that a transmission buffer at theSeNB 5-2 is above a predetermined threshold, an indication that apredetermined number of data packets (e.g. at least one data packet) hasbeen dropped at the SeNB 5-2, and/or the like. When appropriate, theAMBR module 69 provides (via the X2 module 68) the information obtainedfrom dual connectivity module 65 to the MeNB 5-1.

In the above description, the mobile telephone 3 and the base stations 5are described for ease of understanding as having a number of discretemodules (such as the communications control modules and the dualconnectivity modules). Whilst these modules may be provided in this wayfor certain applications, for example where an existing system has beenmodified to implement the invention, in other applications, for examplein systems designed with the inventive features in mind from the outset,these modules may be built into the overall operating system or code andso these modules may not be discernible as discrete entities. Thesemodules may also be implemented in software, hardware, firmware or a mixof these.

<Operation>

A number of different examples will now be described that illustrate howthe invention can be put into effect using the mobile telephone 3 andthe base stations 5 (as exemplary dual connectivity network points) ofFIG. 1. As discussed above, dual connectivity service can be provided byconfiguring the mobile telephone 3 to communicate with both the MeNB 5-1and at least one SeNB 5-2, using respective communication bearers.

FIG. 5 illustrates (using continuous lines) an exemplary bearerconfiguration for the provision of an SeNB-specific communicationbearer. For comparison, FIG. 5 also illustrates (using dashed lines) anMeNB-specific bearer and a split bearer, the descriptions of which areomitted herein for the sake of simplicity. In FIG. 5, some of theprotocol layers and functions (e.g. control-plane) implemented by thebase stations 5 are also omitted. Whilst FIG. 5 illustrates the downlinkdirection only (as indicated by the arrows), a similar bearerconfiguration may be realised for the uplink direction as well, e.g. byreversing the direction of data transmissions, where appropriate.

In the case of an SeNB-specific bearer, the S1 control-plane (e.g.‘S1-MME’) for the mobile telephone 3 is provided by the MeNB 5-1.Control-plane signaling for the mobile telephone 3 can be exchanged withthe SeNB 5-2 via the base station to base station interface (e.g. X2),when required, or it can be communicated directly between the MeNB 5-1and the mobile telephone 3.

In a conventional or ‘regular’ communication bearer configuration thatmay be used in a both single and dual connectivity scenarios, the MeNB5-1 handles the S1 user-plane for a communication bearer (e.g. acommunication bearer that is associated with carrier F1 of FIG. 1)associated with the mobile telephone 3. Downlink data packets for themobile telephone 3 are received by the MeNB 5-1 at the PDCP layer, andforwarded to the lower layers (i.e. the RLC, MAC, and PHY layers) fortransmission to the mobile telephone 3.

In this case, as indicated by the dashed arrows between the PDCP, RLC,MAC, and PHY layers of the MeNB 5-1, (downlink) user data from the corenetwork 7 is processed within the base station 5-1, and transmitted overthe air interface (using carrier F1) between the base station 5-1 andthe mobile telephone 3 (not shown in FIG. 5) using the services of thePHY layer.

According to the communication bearer configuration of the SCG type thatmay be used in a dual connectivity scenario (shown in continuous linesin FIG. 5), user-plane communication (e.g. a communication bearer thatis associated with carrier F2 of FIG. 1) may be provided for the mobiletelephone 3 via the SeNB 5-2, without involving the MeNB 5-1. In thiscase, downlink data packets can be sent from a remote endpoint over anassociated communication bearer through the core network 7 (e.g. via theS-GW 13) and received at the PDCP layer of the SeNB 5-2. After PDCPprocessing, the data packets are passed to the RLC layer, then to theMAC layer, before they are transmitted to the mobile telephone 3 (notshown in FIG. 5) over the PHY layer of the SeNB 5-2 (using carrier F2).

EXAMPLE 1 First Embodiment

FIG. 6 is an exemplary timing diagram illustrating a procedure performedby elements of the mobile telecommunication system 1.

The procedure begins in step S601, in which the MME 11 provides thevalue of the UE-AMBR parameter to the MeNB 5-1. In this case, theUE-AMBR is provided as part of an initial context setup procedure forthe mobile telephone 3. Although not shown in FIG. 6, it will beappreciated that the MME 11 may be configured to derive the value of theUE-AMBR from subscription data for a user associated with the mobiletelephone 3. Such subscription data may be obtained from another entity,e.g. a Home Subscriber Server (HSS), as appropriate.

Next, the MeNB 5-1 derives the (UE-specific) M_(UE-AMBR) and S_(UE-AMBR)parameters from the UE-AMBR, e.g. such that the sum of the M_(UE-AMBR)and the S_(UE-AMBR) does not exceed the value of the UE-AMBR. Forexample, the MeNB 5-1 may be configured to distribute, at leastinitially, the aggregated maximum data rate (UE-AMBR) equally betweenthe base stations 5-1 and 5-2, i.e. both the M_(UE-AMBR) and theS_(UE-AMBR) may be set to 50% of the UE-AMBR associated with the mobiletelephone 3. However, the MeNB 5-1 may also be configured to allocate alarger part (percentage) of the aggregated maximum data rate to one basestation than the part of the aggregated maximum data rate it allocatesto the other base station. As generally shown in step S603, the MeNB 5-1and SeNB 5-2 are thus able to apply their respective M_(UE-AMBR) andS_(UE-AMBR) parameters for the mobile telephone's 3 communications viathat base station 5-1 and 5-2.

In step S605, which may be performed e.g. in response to a request(shown at S604) and/or periodically, the SeNB 5-2 (using its AMBR module69) determines a data rate for the (SeNB-specific) communication bearers(e.g. non-GBR bearers) associated with the mobile telephone 3 (via theSeNB 5-2). Once the data rate associated with the mobile telephone 3 hasbeen determined, the SeNB 5-2 (using its X2 module 68) generates andsends, in step S607, an appropriately formatted signaling message (e.g.an ‘E-RAB Status Report’ X2 message) to the MeNB 5-1, and includes inthis message (e.g. in a suitable information element thereof)information identifying the mobile telephone's 3 data rate.

In step S609, the MeNB 5-1 (using its AMBR module 69), derives updated(UE-specific) M_(UE-AMBR) and S_(UE-AMBR) parameters (e.g. such thatUE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)) by taking into account the receivedinformation identifying the mobile telephone's 3 data rate at the SeNB5-2.

For example, the MeNB 5-1 (using its AMBR module 69) may increase thevalue of the S_(UE-AMBR) parameter (and simultaneously decrease thevalue of the M_(UE-AMBR) parameter such thatUE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)) when the information received from theSeNB 5-2 indicates that the mobile telephone's 3 data rate at the SeNB5-2 is likely to exceed the currently enforced S_(UE-AMBR) (configuredat S603), and the AMBR module 69 of the MeNB 5-1 determines that theMeNB's 5-1 data rate does not exceed the data rate allowance(M_(UE-AMBR)) associated with the mobile telephone 3. Similarly, theMeNB 5-1 (using its AMBR module 69) may increase the value of theM_(UE-AMBR) parameter and simultaneously decrease the value of theS_(UE-AMBR) parameter (such that UE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)) whenthe information received from the SeNB 5-2 indicates that the mobiletelephone's 3 data rate at the SeNB 5-2 does not exceed the currentlyenforced S_(UE-AMBR) (configured at S603), and the AMBR module 69 of theMeNB 5-1 determines that the MeNB's 5-1 data rate is likely to exceedthe data rate allowance (M_(UE-AMBR)) associated with the mobiletelephone 3.

Once an updated S_(UE-AMBR) parameter is derived by the MeNB 5-1, theMeNB 5-1 (using its AMBR module 69) generates and sends, at step S611,an appropriately formatted signaling message to the SeNB 5-2 (over theX2 interface), and includes in this message the updated S_(UE-AMBR).

In step S613, the SeNB 5-2 (using its AMBR module 69) starts to applythe updated S_(UE-AMBR) parameter to the mobile telephone's 3 subsequentcommunications via the SeNB 5-2. Similarly, as shown in step S615, theMeNB 5-1 (using its AMBR module 69) also starts to apply the updatedM_(UE-AMBR) parameter to the mobile telephone's 3 subsequentcommunications via the MeNB 5-1.

EXAMPLE 2 Second Embodiment

FIG. 7 illustrates a modification of the procedure shown in FIG. 6. Inthis case, steps S701 and S703 correspond to S601 and S603,respectively, thus their description is omitted herein.

However, in this example, as generally shown at step S705, the SeNB 5-2(using its dual connectivity module 65) determines that a predeterminednumber of data packets (e.g. at least one data packet) has been dropped(i.e. failed to be sent) for the mobile telephone 3, due to theenforcement of the associated S_(UE-AMBR) parameter.

Therefore, the SeNB 5-2 2 (using its X2 module 68) generates and sends,in step S707, an appropriately formatted signaling message (e.g. an‘E-RAB Status Report’ X2 message) to the MeNB 5-1, and includes in thismessage (e.g. in a suitable information element thereof) an indicationthat one or more data packets for the mobile telephone 3 have beendropped (could not be delivered) due to data rate enforcement.

In step S709, by taking into account the received indication, the MeNB5-1 (using its AMBR module 69), derives updated (UE-specific)M_(UE-AMBR) and S_(UE-AMBR) parameters (e.g. such thatUE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)).

For example, the MeNB 5-1 (using its AMBR module 69) may increase thevalue of the S_(UE-AMBR) parameter (and simultaneously decrease thevalue of the M_(UE-AMBR) parameter such thatUE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)) when the SeNB's 5-2 message indicatesthat a predetermined amount of data packets have been dropped (assumingthat the MeNB's 5-1 data rate does not exceed the data rate allowance(M_(UE-AMBR)) associated with the mobile telephone 3). Similarly, theMeNB 5-1 may decrease the value of the S_(UE-AMBR) parameter (andsimultaneously increase the value of the M_(UE-AMBR) parameter such thatUE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)) when the SeNB's 5-2 message indicatesthat no data packets have been dropped (e.g. since applying the currentS_(UE-AMBR) parameter and/or since a preceding notification was sent bythe SeNB). Advantageously, the MeNB 5-1 may be able to increase (e.g.gradually) its own data rate allocation (M_(UE-AMBR)) for the mobiletelephone 3 as long the mobile telephone's 3 communications via the SeNB5-2 remain unaffected (e.g. no packets are dropped at the SeNB 5-2).

EXAMPLE 3 Third Embodiment

FIG. 8 illustrates another exemplary modification of the procedure shownin FIG. 6. In this case, steps S801 and S803 correspond to S601 andS603, respectively, thus their description is omitted herein.

However, in this example, as generally shown at step S805, the SeNB 5-2(using its dual connectivity module 65) determines that the status ofits transmission buffer meets a predetermined trigger (e.g. thetransmission buffer and/or processing time is above a predeterminedthreshold). It will be appreciated that such predetermined trigger mayresult from the enforcement of the S_(UE-AMBR) parameter associated withthe mobile telephone 3.

Therefore, the SeNB 5-2 2 (using its X2 module 68) generates and sends,in step S807, an appropriately formatted signaling message (e.g. an‘E-RAB Status Report’ X2 message) to the MeNB 5-1, and includes in thismessage (e.g. in a suitable information element thereof) informationrelating to the status of its transmission buffer (for the mobiletelephone 3). It will be appreciated that the information relating tothe status of the SeNB's 5-2 transmission buffer may also be sentperiodically, i.e. regardless whether or not a trigger has been detectedat step S805.

In step S809, by taking into account the received information relatingto the status of the SeNB's 5-2 transmission buffer, the MeNB 5-1 (usingits AMBR module 69), derives updated (UE-specific) M_(UE-AMBR) andS_(UE-AMBR) parameters (e.g. such that UE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)).

For example, the MeNB 5-1 (using its AMBR module 69) may increase thevalue of the S_(UE-AMBR) parameter (and simultaneously decrease thevalue of the M_(UE-AMBR) parameter such thatUE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)) when the SeNB's 5-2 message indicatesthat SeNB's 5-2 transmission buffer is over a predetermined threshold(assuming that the MeNB's 5-1 data rate does not exceed the data rateallowance (M_(UE-AMBR)) associated with the mobile telephone 3).Similarly, the MeNB 5-1 may decrease the value of the S_(UE-AMBR)parameter (and simultaneously increase the value of the M_(UE-AMBR)parameter such that UE-AMBR=M_(UE-AMBR)+S_(UE-AMBR)) when the SeNB's 5-2message indicates that the SeNB's 5-2 transmission buffer is not over(e.g. it is below) a predetermined threshold. Advantageously, the MeNB5-1 may be able to increase (e.g. gradually) its own data rateallocation (M_(UE-AMBR)) for the mobile telephone 3 as long the mobiletelephone's 3 communications via the SeNB 5-2 remain unaffected (e.g.the transmission buffer at the SeNB 5-2 stays below the predeterminedthreshold).

<Modifications and Alternatives>

Detailed embodiments have been described above. As those skilled in theart will appreciate, a number of modifications and alternatives can bemade to the above embodiments whilst still benefiting from theinventions embodied therein.

In the above examples, the MeNB is described to comprise a macro basestation. However, it will be appreciated that the MeNB may comprises anytype of base station, e.g. a pico base station, a femto base station, ahome base station. Further, it will be appreciated that either of thecarriers F1 and/or F2 may be provided via a relay, a remote radio head,and/or the like instead of a base station.

In the above examples, each base station is described to provide asingle carrier (F1 or F2). However, it will be appreciated that eachbase station may provide a plurality of carriers (e.g. the same and/ordifferent set of carriers).

It will be appreciated that whilst the above examples are described withreference to a communication bearer of the SCG type, the description isequally applicable to any other types of communication bearers,including MeNB-specific and/or ‘split’ communication bearers (e.g. asspecified in 3GPP TR 36.842).

In the above description of FIG. 5, there is only one instance of MCGbearer, one instance of SCG bearer, and one instance of split bearershown. However, it will be appreciated that any number and/or any typesof bearers, in any combination may be provided for a particular UE. Forexample, multiple bearers of each type and/or any combination of bearersof different types may be provided. In any case, the actual bearerconfiguration is based on the associated QCI value. For example, ifthere are two SCG bearers (both bearers being non-GBR) for a particularUE, then the aggregate data rate on these two SCG bearers should notexceed the S_(UE-AMBR) associated with the UE. In another example, ifthere is one split bearer and one SCG bearer for a particular UE (bothbearers being non-GBR), then the aggregate data rate on the SCG bearerand on the SeNB part of the split bearer should not exceed theS_(UE-AMBR) associated with the UE.

In the above embodiments, the MeNB is described to derive (and provideto the SeNB) an updated S_(UE-AMBR) parameter by taking into account theinformation (data rate, packet drop indication, and/or the like)received from the SeNB. However, it will be appreciated that the MeNBmay also be configured to send an indication to the SeNB to discard orignore, at least temporarily, any previously sent S_(UE-AMBR) parameter(instead of deriving an updated S_(UE-AMBR) parameter). This maybeneficially allow the SeNB to avoid unnecessarily dropping data packetsfor the mobile telephone. In this case, the SeNB may be configured tosuspend enforcement of the S_(UE-AMBR) parameter at least until apredetermined time period, until receipt of a new S_(UE-AMBR) parameterfrom the MeNB, and/or until the SeNB has emptied or reduced below athreshold the amount of data held in its transmit buffer for the mobiletelephone.

In the above description of FIG. 6, the SeNB is described to generateand send an ‘E-RAB Status Report’ signaling message formatted inaccordance with the X2 application protocol. However, it will beappreciated that a different message and/or a different applicationprotocol may also be used. For example, the SeNB may be configured toinclude information relating to its data rate in a suitable field (e.g.an ‘enforcement result’ field, ‘AMBR information’ field, ‘data rate’field and/or the like) in a Frame Protocol message.

It will be appreciated that the SeNB may generate and send the data rateinformation (at step S607) either periodically and/or when apredetermined trigger is met. Such a predetermined trigger may includeany of the following:

-   -   the data rate for the mobile telephone is higher than (or equal        to) the associated S_(UE-AMBR);    -   the data rate for the mobile telephone is higher than (or equal        to) the associated S_(UE-AMBR) minus an offset (e.g. 10% below        the S_(UE-AMBR))    -   expiry of an associated timer;    -   transmission buffer being over a predetermined threshold (which        may be indicative of an insufficient for S_(UE-AMBR) being        configured for the mobile telephone);    -   a sudden change (e.g. increase/decrease) in the data rate        required for the mobile telephone;    -   the SeNB has additional capacity that can be allocated to        communication bearers associated with the mobile telephone;    -   receipt of a data rate error indication from the mobile        telephone (or from lower layers of the SeNB); and    -   receipt of a request from the MeNB (e.g. as shown at step S604).

It will be appreciated that when the SeNB sends the packet dropindication to the MeNB (at step S707), it may also send informationidentifying the data rate for the mobile telephone. In other words,steps S607 and S707 may be combined.

It will also be appreciated that the SeNB may be configured to provide,to the MeNB over the X2 interface, information identifying the number ofdata packets discarded during a given time period (e.g. at the RLCand/or MAC layers). Based on this information, the MeNB may be able todetermine a measure of an associated “Packet Discard Rate” at the SeNB(for the mobile telephone), and update the M_(UE-AMBR) and/orS_(UE-AMBR) accordingly. For example, the MeNB may increase the value ofthe S_(UE-AMBR) by at least the determined “Packet Discard Rate” for themobile telephone (up to the associated UE-AMBR).

It will be appreciated that the base stations (MeNB and SeNB) may beconfigured to provide each other information relating to their own datarates for the mobile telephone served by both base stations. Further, itwill be appreciated that the MeNB may be configured to determineunder-utilisation of its communication resources allocated for themobile telephone (e.g. the MeNB may be configured to determine that themobile telephone's data rate via the MeNB is below a thresholdvalue/percentage and/or it is below the associated M_(UE-AMBR) minus anoffset). In this case, the MeNB may be configured to provide anappropriate indication to the SeNB, which in turn may cause the SeNB toexceed/ignore, at least temporarily, the associated S_(UE-AMBR) for themobile telephone (whilst still enforcing the UE-AMBR value, i.e.M_(UE-AMBR)+S_(UE-AMBR)).

Alternatively, the MeNB may be configured to inform the MME about thecurrent values of the M_(UE-AMBR) and/or the S_(UE-AMBR) to be enforcedat the MeNB and the SeNB, respectively. In this case, the MME may beconfigured to forward the values of the M_(UE-AMBR) and/or theS_(UE-AMBR) to the S-GW and the S-GW may be configured to forward thevalues of the M_(UE-AMBR) and/or the S_(UE-AMBR) to the P-GW.Advantageously, the P-GW may be able to perform the enforcement of theM_(UE-AMBR) and/or the S_(UE-AMBR) parameters (e.g. by performing datarate enforcement with the value of M_(UE-AMBR) for communication bearersprovided via the MeNB and performing data rate enforcement with thevalue of S_(UE-AMBR) for communication bearers provided via the SeNB).This alternative may require a new (or modified) signaling message to besent between the MeNB and the MME over the S1 interface (i.e. for theprovision of the M_(UE-AMBR) and/or the S_(UE-AMBR) to the MME).

The base station (e.g. MeNB) may comprise means for deriving a bit ratespecific to the base station, wherein the sum of the bit rate specificto the base station and the bit rate specific to the further basestation (e.g. SeNB) does not exceed the aggregate maximum bit ratespecific to the user communication device.

The information relating to a data rate required for the usercommunication device via said further base station may comprise at leastone of: information relating to a data rate (e.g. non-GBR data rate)arriving at said further base station for the user communication device,an indication of a data loss associated with the user communicationdevice at said further base station, and information identifying abuffer status for said user communication device.

The information relating to a data rate required for said usercommunication device via said further base station may compriseinformation relating to data packets transmitted over one or morenon-guaranteed bit rate communication bearers associated with said usercommunication device.

The base station may be configured to operate as a master base stationof said dual connectivity configuration and the further base station maybe configured to operate as a secondary base station of said dualconnectivity configuration.

The generating means (of the base station) may be operable to, when saidinformation relating to a required data rate (via the further basestation) is not available, generate an initial bit rate specific to thefurther base station, to be used in enforcement of a maximum datathroughput over said at least one communication bearer via said furtherbase station, based on the aggregate maximum bit rate specific to theuser communication device. In this case, the providing means may beoperable to provide the initial bit rate specific to said further basestation to said further base station (e.g. prior to said obtaining meansobtaining said information relating to a data rate required for the usercommunication device via said further base station).

The base station may further comprise means for controlling theestablishment of said at least one communication bearer between the corenetwork and the user communication device via said further base station;wherein said establishment of said at least one communication bearer maycomprise providing, to said further base station, said initial bit ratespecific to said further base station.

The providing means may be configured to provide, to said further basestation, said information identifying said bit rate specific to saidfurther base station over a base station to base station interface (e.g.an X2 interface).

The providing means (of the secondary base station) may be operable toprovide said information to said master base station periodically and/orupon request by the master base station and/or upon detecting apredetermined trigger. The providing means may be operable to providesaid information by sending at least one message to said master basestation over a base station to base station interface.

In the above embodiments, a mobile telephone based telecommunicationssystem was described. As those skilled in the art will appreciate, thesignaling techniques described in the present application can beemployed in other communications system. Other communications nodes ordevices may include user devices such as, for example, personal digitalassistants, laptop/tablet computers, web browsers, etc.

In the embodiments described above, the mobile telephone and the basestations will each include transceiver circuitry. Typically thiscircuitry will be formed by dedicated hardware circuits. However, insome embodiments, part of the transceiver circuitry may be implementedas software run by the corresponding controller.

In the above embodiments, a number of software modules were described.As those skilled in the art will appreciate, the software modules may beprovided in compiled or un-compiled form and may be supplied to the basestations as a signal over a computer network, or on a recording medium.Further, the functionality performed by part or all of this software maybe performed using one or more dedicated hardware circuits.

This invention has been described above by way of the embodiment, butthis invention is not limited to the embodiment described above. Variouschanges that can be understood by a person skilled in the art can bemade to the configuration and details of this invention within the scopeof this invention. Various other modifications will be apparent to thoseskilled in the art and will not be described in further detail here.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1414139.4, filed on Aug. 8, 2014,the disclosure of which is incorporated herein in its entirety byreference.

1. A base station configured to operate as a master base station of adual connectivity configuration in which a control-plane connection fora user equipment (UE) is provided via the master base station and atleast one communication bearer between a core network and the UE isprovided via at least one secondary base station, different to saidmaster base station, said base station comprising: a memory storinginstructions; and a processor configured to execute the instructions to:obtain information relating to a data rate for said UE via saidsecondary base station; generate information identifying a bit ratespecific to said secondary base station, for use in enforcement of anaggregate maximum data throughput for said UE via said secondary basestation, wherein said bit rate specific to said secondary base stationis generated based on: an aggregate maximum bit rate (AMBR) specific tosaid UE; and said obtained information relating to the data rate forsaid UE via said secondary base station; and provide, to said secondarybase station, said information identifying said bit rate specific tosaid secondary base station; wherein said information relating to thedata rate for said UE via said secondary base station comprises at leastone of: information relating to a data rate at said secondary basestation for said UE relative to an AMBR applicable at said secondarybase station for said UE, an indication of a data loss associated withsaid UE at said secondary base station, and information identifying abuffer status for said UE.
 2. The base station according to claim 1,wherein the processor is further configured to obtain said informationrelating to a data rate for said UE via said secondary base station fromthe secondary base station, using X2 application protocol signaling. 3.The base station according to claim 2, wherein said X2 applicationprotocol signaling comprises an AMBR status report from the secondarybase station.
 4. The base station according to claim 1, wherein saidinformation relating to the data rate for said UE via said secondarybase station comprises information relating to data packets transmittedover one or more non-guaranteed bit rate communication bearersassociated with said UE.
 5. The base station according to claim 1,wherein the processor is further configured to provide, to saidsecondary base station, said information identifying said bit ratespecific to said secondary base station over a base station to basestation interface.
 6. A base station configured to operate as asecondary base station of a dual connectivity configuration in which acontrol-plane connection for a user equipment (UE) is provided via amaster base station, different to said secondary base station, and atleast one communication bearer between a core network and the UE isprovided via said secondary base station, said base station comprising:a memory storing instructions; and a processor configured to execute theinstructions to: determine a data rate for said UE via said secondarybase station; provide, to said master base station, information relatingto said determined data rate for said UE via said secondary basestation; and receive, from said master base station, informationidentifying a bit rate specific to said secondary base station, whereinsaid bit rate specific to said secondary base station is based on: i) anaggregate maximum bit rate (AMBR) specific to said UE; and ii) said datarate for said UE via said secondary base station; wherein saidinformation relating to said determined data rate for said UE via saidsecondary base station comprises at least one of: information relatingto a data rate arriving at said secondary base station for said UErelative to an AMBR applicable at said secondary base station for saidUE, an indication of a data loss associated with said UE at saidsecondary base station, and information identifying a buffer status forsaid UE.
 7. The base station according to claim 6, wherein the processoris further configured to provide said information relating to saiddetermined data rate to said master base station using X2 applicationprotocol signaling.
 8. The base station according to claim 7, whereinsaid X2 application protocol signaling comprises an AMBR status report.9. The base station according to claim 6, wherein said informationrelating to said determined data rate comprises information relating todata packets transmitted over one or more non-guaranteed bit ratecommunication bearers associated with said UE.
 10. The base stationaccording to claim 6, wherein the processor is further configured toreceive, from said master base station, said information identifying abit rate specific to said secondary base station over a base station tobase station interface.
 11. A method performed by a base stationconfigured to operate as a master base station of a dual connectivityconfiguration in which a control-plane connection for a user equipment(UE) is provided via the master base station and at least onecommunication bearer between a core network and the UE is provided viaat least one secondary base station, different to said master basestation, the method comprising: obtaining information relating to a datarate for said UE via said secondary base station; generating informationidentifying a bit rate specific to said secondary base station, for usein enforcement of an aggregate maximum data throughput for said UE viasaid secondary base station, wherein said bit rate specific to saidsecondary base station is generated based on: i) an aggregate maximumbit rate (AMBR) specific to said UE; and ii) said obtained informationrelating to the data rate for said UE via said secondary base station;and providing, to said secondary base station, said informationidentifying said bit rate specific to said secondary base station;wherein said information relating to the data rate for said UE via saidsecondary base station comprises at least one of: information relatingto a data rate at said secondary base station for said UE relative to anAMBR applicable at said secondary base station for said UE, anindication of a data loss associated with said UE at said secondary basestation, and information identifying a buffer status for said UE.
 12. Amethod performed by a base station configured to operate as a secondarybase station of a dual connectivity configuration in which acontrol-plane connection for a user equipment (UE) is provided via amaster base station, different to said secondary base station, and atleast one communication bearer between a core network and the UE isprovided via said secondary base station, the method comprising:determining a data rate for said UE via said secondary base station;providing, to said master base station, information relating to saiddetermined data rate for said UE via said secondary base station; andreceiving, from said master base station, information identifying a bitrate specific to said secondary base station, wherein said bit ratespecific to said secondary base station is based on: i) an aggregatemaximum bit rate (AMBR) specific to said UE; and ii) said data rate forsaid UE via said secondary base station; wherein said informationrelating to said determined data rate for said UE via said secondarybase station comprises at least one of: information relating to a datarate arriving at said secondary base station for said UE relative to anAMBR applicable at said secondary base station for said UE, anindication of a data loss associated with said UE at said secondary basestation, and information identifying a buffer status for said UE.